1. Field of the Invention
The present invention relates to a thin film forming apparatus and a thin film forming method, which require to press a substrate and a sheet film against each other within a thin film forming chamber so that a thin film, such as an insulation film, disposed on the sheet film in advance is transferred onto the substrate and a thin film is accordingly disposed on the substrate.
2. Description of the Related Art
Over the recent years, it has became necessary to use a thin film forming method suitably applicable to a large area size as wafers for the manufacture of LSIs have became larger in diameter, liquid crystal panels have became larger in area size, etc. In addition, in the field of multilevel interconnections techniques for manufacturing LSIs, as the surface of an insulation film needs be planarized accurately to realize multilevel interconnections. It is not only necessary to handle an increase in surface area but surface planarization techniques to form thin films as well are in an increasing demand. In an effort to satisfy these requirements, thin film forming techniques for forming a thin film on a substrate by a pressure transfer method have been proposed.
This type of thin film forming apparatus may be an apparatus which is described in Japanese Patent Application Laid-Open Gazette No. H10-189566 for instance. In this apparatus, a specimen holder comprising a built-in heater is disposed within a thin film forming chamber which is located inside a processing container. A semiconductor wafer, a glass substrate for liquid crystal panel or the like (hereinafter referred as “substrate”) on which a thin film is to be formed can be held on the specimen holder. Further, a transfer plate is disposed below the specimen holder so as to face the specimen holder within the thin film forming chamber, and holds the sheet film with the thin film, which is disposed on the sheet film so that the thin film faces to the substrate. Like the specimen holder, the transfer plate as well comprises a heater, so that it is possible to heat up the sheet film which is held on the transfer plate.
A vacuum pump is linked to the thin film forming chamber. The substrate is held on the specimen holder and the sheet film is held on the transfer plate, and after the thin film forming chamber is closed air-tight, the thin film forming chamber is evacuated by the vacuum pump. Following this, while evacuating and depressurizing the thin film forming chamber by the vacuum pump, the specimen holder holding the substrate and the transfer plate holding the sheet film are moved closer to each other. Thus, the substrate and the sheet film are pressed against each other, and the thin film on the sheet film is transferred onto the substrate. As the thin film is disposed on the substrate in this manner, after moving the substrate and the sheet film back to their original positions, the thin film forming chamber is returned back to the atmospheric pressure. Finally, the substrate with the thin film and the sheet film without the thin film are unloaded out from the processing container.
By the way, in a conventional thin film forming apparatus of the pressure transfer method, after setting the substrate and the sheet film respectively to the specimen holder and the transfer plate, the vacuum pump starts to evacuate and depressurize the thin film forming chamber. Simultaneously with evacuating and depressurizing, transfer of the thin film to the substrate is executed. However, in the conventional apparatus, while the thin film forming chamber is simply evacuated and depressurized by the vacuum pump, there is no special consideration given on the pressure inside the thin film forming chamber (degree of vacuum) as it is before and during the transfer, thus leaving a room for improvement for excellent creation of a thin film. For instance, although the thin film needs to have a certain level of fluidity so as to be transferred favorably to the substrate, as the pressure inside the thin film forming chamber is largely reduced prior to the start of the transfer, a solvent component contained in the material of the thin film evaporates in a great quantity owing to the lowered pressure inside the thin film forming chamber. The fluidity of the thin film therefore would have deteriorated by the time the transfer starts, thereby making it impossible to favorably transfer the thin film to the substrate in some cases. Conversely, but for sufficient depressurization of the thin film forming chamber during transfer, the transfer of the thin film to the substrate could leave a void between a pattern formed in the substrate, such as a contact hole, and the thin film, in which case excellent transfer becomes impossible. Thus, an optimal value of the pressure inside the thin film forming chamber is different between before and during the transfer, and hence, in order to execute excellent transfer, it is important to flexibly and precisely control the pressure inside the thin film forming chamber. Despite this, such pressure control is difficult in the conventional apparatus.